It is desired that a motor control apparatus causes a motor position and speed to follow target values such as a position target value and a speed target value at high speed and high accuracy. To realize this, two degrees of freedom control obtained by combining feed forward control and feedback control is used. As a method of further increasing speed and accuracy, a control method for pre-reading and using not only a present target value but also a future target value is sometimes used. Further, simultaneously with the increases in the speed and the accuracy, it is also necessary to suppress residual vibration during a stop that occurs because of mechanical resonance and the like. Vibration suppression is realized by damping control for designing a feed forward control system to reduce a signal component at a vibration frequency (a resonance frequency) of an industrial machine.
Usually, to cause a motor to follow a target value at higher speed and higher accuracy, it is necessary to generate larger torque. When control for actively suppressing residual vibration during a stop is performed, larger torque is necessary and a change amount of the torque increases. However, there is a limit for a control input of torque that the motor can generate, and also for an electric current applied to the motor necessary for generating the torque, or the like. The change amount of the torque is closely related to a voltage generated in a motor control apparatus. When the change amount of the torque increases, the voltage increases and voltage saturation occurs. When the change amount of the torque increases, a shock given to a machine system also increases. Accordingly, there is also a limit in a change amount of the control input such as the change amount of the torque. Therefore, there is a desire for control that can follow a target value at high speed and high accuracy and suppress residual vibration during a stop while satisfying constraints on a control input and a change amount.
For example, Patent Literature 1 discloses an electric motor control apparatus that performs, using target values two steps ahead or four steps ahead, prediction control in which target values M (M>4) steps ahead are necessary. In the related art, a control operation is simplified by using only the target values two steps or four steps ahead. An overshoot during acceleration and deceleration is reduced and followability during fixed speed is improved by calculating speed feed forward and torque feed forward from these values and using the speed feed forward and the torque feed forward for control.
A servo control apparatus described in Patent Literature 2 includes a changeover switch and, when the changeover switch is ON, uses feedback control or two degrees of freedom control in which a prediction controller is used as a feedback controller and, when the changeover switch is OFF, switches the feedback control of only position proportional control to improve performance. In the related art, when a controlled object requests highly accurate followability, the servo control apparatus turns on the changeover switch. When a target command increase value changes, the servo control apparatus turns off the changeover switch. To make control inputs before and after the switching continuous, the servo control apparatus linearly interpolates the control inputs before and after the switching using a filter function unit.